Clinical applications in which a medical instrument has to be guided into the body of a patient are becoming widespread. Notably the growing interest in minimal-invasive methods for the treatment of cardiac diseases necessitates the development of methods and devices allowing the physician to guide a medical instrument to predetermined positions inside or outside the heart. In electrophysiology for example, it is necessary to guide a catheter to a plurality of predetermined positions on the ventricular or atrial walls in order to measure an electrical pulse or to burn wall tissues.
U.S. Pat. No. 6,587,709 discloses a system for guiding a medical instrument in the body of a patient. Such a system acquires a live 3D ultrasound image data set using an ultrasound probe. An advantage of acquiring a 3D image data set is to get depth information. An advantage of using a live 3D ultrasound image modality is that the surrounding anatomy is visible, which facilitates the guidance of the medical instrument by the physician. The system further comprises localization means for localizing the medical instrument within the 3D ultrasound data set, which locates three ultrasound receivers mounted on the medical instrument relatively to said ultrasound probe. Such a localization allows an automatic selection of a plane to be imaged, which comprises at least a section of the medical instrument. Therefore no readjustment of the ultrasound probe position by hand is necessary.
A first drawback of such a 3D ultrasound data set is that it has a narrow viewing field, which does not cover the whole part of the patient body concerned by a catheter introduction and placement. Therefore, for guiding the catheter during the whole procedure, the ultrasound probe has to be moved several times. At each displacement, a pre-operative step of locating the ultrasound probe in a referential of the interventional room is needed, because the location of the catheter is measured relatively to the ultrasound probe location. Such a pre-operative step may delay and complicate the interventional procedure.
A second drawback of the ultrasound imaging modality is that it has a low resolution Therefore, the acquired 3D ultrasound data set does not give an image of the catheter and its surrounding of acceptable quality.
A third drawback of the ultrasound imaging modality is that there are some zones of the patient body where the thoracic cage blocks the ultrasound scan and no exploitable image can be output.